It has recently been recognised that long chain polyunsaturated fatty acids provide extensive nutritional and health benefits in human health (Uauy-Dagach, R. and Valenzuela, A. Nutrition Reviews 1996; 54, 102-108; Ruxton, C. H. S., Reed, S. C., Simpson, J. A. and Millington, K. J. 2004; J. Human Nutr. Dietet. 17, 449-459).
For example, omega-3 fatty acids have been documented as contributing to the prevention of coronary heart disease, hypertension, type 2 diabetes, rheumatoid arthritis, Crohn's disease and obstructive pulmonary disease (Simopoulos A P, Am J Clin Nutr, 1999; 70:560-569).
Recognition of the potential benefits of these lipids has stimulated interest in foods and nutraceuticals that contain them. However, including lipids such as omega-3 fatty acids into food products gives rise to major formulation challenges. Many lipids are sensitive to heat, light and oxygen and undergo oxidative damage very quickly. Fatty acid oxidation is a major cause of food deterioration which can affect the flavour, aroma, texture, shelf life and colour of food.
Besides producing undesirable characteristics in the food such as off-flavour, oxidative damage can eliminate the beneficial biological activity of an oxidisable lipid. There is also a potential for health damage by increasing free radical formation in the body. Accordingly, if oxidisable lipids such as omega-3 fatty acids are to be successfully incorporated into food products, these negative characteristics must be avoided.
One way of reducing oxidative damage is to encapsulate the oxidisable lipid so as to reduce its contact with oxygen, trace metals and other substances that attack the double bonds and other susceptible locations of the oxidisable lipid. To this end, oxidisable lipids have been combined with a number of other substances including other oils, polysaccharides and proteins.
Many existing encapsulation systems for fatty acids and other lipids use polysaccharides and gelatine to form microcapsules; see for example, British patent GB 1,236,885. Because of their relatively large size, these microcapsules can sediment in low-viscosity products and hence are unsuitable for application in beverages, particularly long shelf-life, heat-treated food products.
In U.S. Pat. No. 4,895,725 microcapsules of fish oil are produced by encapsulating the oil within a non-oil soluble enteric coating. Although palatable, the resulting capsules are not heat stable and are unstable at a pH higher than 7. This greatly limits their application in a wide range of food products.
Proteins have also been used to encapsulate oxidisable lipids and have been partially successful in reducing the odour of strong smelling lipids. For example; Patent Application JP 60-102168 describes a fish oil emulsion incorporating hydrophilic proteins that is able to suppress the fishy smell. However, the composition is vulnerable to oxidation and must still contain an antioxidant. Oxidation mechanisms in complex food systems are different from those in bulk oils. Compounds that are efficient antioxidants in a bulk oil may have pro-oxidant activity in complex food systems. It may therefore be desirable to avoid incorporation of antioxidant compounds if possible. Proteins are also generally unstable when heated so protein-based emulsions may be unsuitable for many food applications.
PCT publication WO 01/80656 describes a composition that comprises a milk or aqueous portion, a protecting oil such as oat oil or oat bran oil and polyunsaturated lipid stabilised with soy protein. The emulsion is reported to demonstrate a lower oxidation rate than an unstabilised emulsion because of the antioxidant properties of the protecting oil.
PCT publication WO 96/19114 describes a water-in-oil emulsion containing a fish oil. The fat phase of the emulsion comprises unhydrogenated fish oil and an antioxidant. The aqueous phase must not contain any ingredient that can react or catalyse a reaction with the components of the fat phase. The specification reports that milk proteins contain ingredients which may react with or act as catalysts for a reaction with the fish oil and/or antioxidant causing a metallic off-flavour or fishy taste. It is therefore suggested that the use of these proteins in the emulsion is to be avoided.
Milk proteins have, however, been used in combination with carbohydrates to encapsulate oxygen-sensitive oils in US Patent Application 20030185960. The specification describes heating a milk protein such as casein, soy or whey with a carbohydrate containing a reducing group. The resulting Maillard reaction products are mixed with the oil and homogenised. Unfortunately, Maillard reaction products are considered to have a negative effect on human health. In addition, the high sugar content of the resulting emulsion precludes its use in low calorie and/or low carbohydrate savory products.
Consequently, it is an object of the invention to provide an improved or alternative emulsion for encapsulating at least one oxidisable lipid that alleviates at least some of the disadvantages discussed above, or at least provides the public with a useful choice.